In this proposal, the investigator will examine the ability of defective HIV-1 vectors to present HIV-1 antigens to the immune system. The investigator proposes some of the positive features of live attenuated lentivirus vaccines might be mimicked by defective HIV-1 vectors while alleviating concerns over safety. Specific Aims include examining whether HIV-1 antigens can be expressed by defective HIV-1 vectors in an animal model and to determine the ability of these vectors to elicit specific antiviral immune responses; i.e., neutralizing antibodies and cytotoxic T-lymphocytes.